1. Field of the Invention
The present invention relates to an improved process for preparing an aromatic polymer which has excellent heat resistance and thermal stability and improved color. More particularly, it relates to a process for preparing the aromatic polymer at remarkably improved reaction velocity.
2. Description of Prior Art
It has been known to prepare an aromatic polymer by reacting a dialkali metal salt of diphenol with a dihalogenobenzenoid compound containing an electron withdrawing group in at least one position ortho or para to each of the halogen atoms in the absence of a solvent, in U.S. Pat. No. 3,886,120.
Although the aromatic polymer having good heat resistance and thermal stability and improved color can be obtained by the process, the reaction velocity has been remarkably slow. Accordingly, it has the disadvantage that the reaction should be carried out by mixing the mixture having high viscosity for a long period. When the process is worked in an industrial scale, the disadvantage has been serious and sometimes it has been fatal.
It has been also known to prepare the aromatic polymers by solution polymerization in an anhydrous polar solvent such as dimethyl sulfoxide, dimethyl sulfone or tetrahydrothiophene-1,1-dioxide (British Pat. No. 1,078,234) or dimethyl acetamide, tetramethyl urea or hexamethyl phosphamide (Japanese Pat. No. 18146/1971). These processes can be advantageously worked in an industrial scale by relatively easy operation from the viewpoint of equipments.
However, the aromatic polymers prepared by these processes have brown color, so that the light transmittance of polymers are relatively low. Accordingly, the polymers had no advantage of transparent polymer and the appearance which is one of the important values as commercial resins has been substantially lost.